Controlled generation of higher-order Poincare sphere beams from a laser

TL;DR

This paper introduces a novel laser design capable of directly generating any state on the higher-order Poincaré sphere by controlling geometric phase within the cavity, enabling versatile vector vortex beam production.

Contribution

A new laser architecture that uses geometric phase control to produce all higher-order Poincaré sphere states directly at the source.

Findings

Able to generate pure OAM modes from a standard laser cavity

Demonstrated creation of radially and azimuthally polarized beams

Broken OAM degeneracy in the laser cavity

Abstract

The angular momentum state of light can be described by positions on a higher-order Poincar\'e (HOP) sphere, where superpositions of spin and orbital angular momentum states give rise to laser beams that have found many applications, including optical communication, quantum information processing, microscopy, optical trapping and tweezing and materials processing. Many techniques exist to create such beams but none to date allow their creation at the source. Here we report on a new class of laser that is able to generate all states on the HOP sphere. We exploit geometric phase control with a non-homogenous polarization optic and a wave-plate inside a laser cavity to map spin angular momentum (SAM) to orbital angular momentum (OAM). Rotation of these two elements provides the necessary degrees of freedom to traverse the entire HOP sphere. As a result, we are able to demonstrate that the OAM degeneracy of a standard laser cavity may be broken, producing pure OAM modes as the output, and that generalized vector vortex beams may be created from the same laser, for example, radially and azimuthally polarized laser beams. It is noteworthy that all other aspects of the laser cavity follow a standard design, facilitating easy implementation.